Technical Field
The disclosed technology relates to electronic systems and, in particular, to DC-to-DC voltage converters.
Description of Related Technology
One type of device that converts one direct current (“DC”) voltage level to another DC voltage level may be referred to as a DC-to-DC converter (DC-DC converter). DC-DC converters can be included in battery-operated devices such as mobile telephones, laptop computers, etc., in which the various subsystems of the device require several discrete voltage levels. In some types of devices, such as a mobile telephone that operates in a number of different modes, it can be desirable to supply certain elements, such as power amplifiers, with a supply voltage at a more efficient level for the mode of operation, rather than waste power and accordingly drain the battery prematurely. In such devices, it can be desirable to employ a DC-DC converter that can generate a number of discrete voltage levels.
Some example DC-DC converters include switched-mode DC-DC converters and DC-DC converters that employ pulse-width modulation (PWM). Switched-mode DC-DC converters can convert one DC voltage level to another DC voltage level by storing the input energy momentarily or temporarily in inductors and/or capacitors and then releasing that energy to the output at a different voltage. The switching circuitry can thus continuously switch between two states or phases: a first state in which a network of inductors and/or capacitors is charging, and a second state in which the network is discharging. The switching circuitry can generate an output voltage that is a fixed fraction of the battery voltage, such as one-third, one-half, two-thirds, etc., where a mode selection signal can be provided as an input to the switching circuitry to control which of the fixed fractions is to be employed. Different configurations of the network of inductors and/or capacitors can be selected by manipulating switches in the network based on the mode selection signal.
The number of discrete output voltages that a switched-mode DC-DC converter can generate can be related to the number of inductors and/or capacitors in the switching circuitry. In a portable, handheld device such as a mobile telephone it can be desirable to minimize size and weight. A DC-DC converter having a relatively large number of inductors and/or capacitors may not be conducive to minimizing the size and weight of a mobile telephone. A PWM-based DC-DC converter can generate a larger number of discrete voltages than a switched-mode DC-DC converter without employing significantly more inductors, capacitors and/or other circuit elements. However, a PWM based DC-DC converter can generate a relatively large spectrum of spurious output signals that can adversely affect the operation of a mobile telephone or other frequency-sensitive device. Filters having relatively large capacitances and/or inductances can be included in a PWM-based DC-DC converter to minimize these spurious signals, but large filter capacitors and/or inductors can be undesirable for at least the reasons relating to size and weight described above.